Method and means for shot peening of tubes

ABSTRACT

In shot-peening the external surface of a tube that is partly straight and partly curved or bent, straight portions of the tube are peened by moving the tube in a straight path through a stationary peening device, while bent portions are peened by holding the tube stationary and moving the peening device about the bend in the tube.

United States Patent Stromstedt et a].

June 3, 1975 METHOD AND MEANS FOR SHOT EENING UB S 6] References Cited [75] Inventors: Sven Sixten Stromstedt; Sven Borje UNITED STATES PATENTS Bystmmi both of Sandvlken, 3,142,590 7/1964 Hergonson 51/320 Sweden 3,531,964 10/1970 Manning 72/53 [7 1 Assignees: Kraftwerk Union Akfiengeseuschaft, 3,668,9l2 6/1972 Baughman 72/53 Mulheim, Ruhr; Mannesmannrohren-werke Primary ExaminerRichard J. Herbst Aktiengesellschaft, Dusseldorf, both Assistant EXaminerGene Crosby f Germany Attorney, Agent, or Firm-Pierce, Scheffler & Parker [22] Filed: May 22, 1974 21 A l N 472 470 [57] ABSTRACT 1 pp O" In shot-peening the external surface of a tube that is partly straight and partly curved or bent, straight porl g" Appllcatlon y Data tions of the tube are peened by moving the tube in a May 30, 1973 Sweden 73076820 straight path through a stationary peening device, while bent portions are peened by holding the tube [52] US. Cl 72/53; 81/8 stationary and moving the peening device about the [51] Int. Cl C2ld 7/06 bend in the tube. [58] Field of Search 72/53; 51/8, 9, 9 331296 7 Claims, 5 Drawing Figures b I 17; 7 0G1 I 75 1 23 I l:'::::: :E, b [fa- F m. ,l;i l fi L: g

METHOD AND MEANS FOR SHOT PEENING OF TUBES This invention relates to shot peening of tubes, and is concerned with shot peening a tube that has a straight portion and a bent portion in such manner that the resulting compressive stresses are uniformly distributed over the surface of the whole tube.

In order to improve the resistance to stress corrosion in the external surface of tubes it is usual to introduce compressive stresses in the surface by means of shot peening. Heretofore, the tubes have been shot peened in straight shape, and any possible bending has been done afterwards. A disadvantage with this is that the bending eliminates some of the compressive stresses that have been formed by the peening. Because of this, it has been desired to peen the tube in a bent state, but previously it has not been possible to find any reliable method and device for obtaining a uniform distribution of the compressive stresses over the whole surface of the tube. It is not practically possible to feed bent portions ofa tube of any considerable length through a stationary peening apparatus. Nor is it possible to keep the tube stationary and move the peening apparatus, because the apparatus is bulky. It has been considered to place a number of peening devices along the tube and hold both the tube and the peening device stationary, but this does not give a sufficiently uniform distribution of the peening effect.

The present invention takes advantage of the fact that certain movements of the workpiece and the apparatus are easy to perform, while other movements are difficult to perform. It is simple to move the tube lengthwise in a straight path. It is also simple to move the shot peening nozzles a short distance because the nozzles are connected with the peening machinery by means of flexible hoses. It is difficult to move the tube with a rotary movement of a vertical axis, because of the great length of the tube. It is also difficult to move the peening nozzles a long way, because this would require a too long connection between the machiner and the nozzles.

The invention is based on the idea of separating the relative movements of the tube and the peening device so that the tube is moved when straight portions are being peened and the peening device is moved when curved portions of the tube are being peened. This separation of the mutual movements of the tube and the peening device means that the movements are limited to those which are easy to perform, i.e. linear movement of the tube and a short movement of the peening device. Such movements that are difficult to perform, i.e. turning of the tube and an extended movement of the peening device, have been eliminated. In this way thereby it has been made possible to shot peen tubes with alternating curved and straight portions so that all parts of the tube are uniformly peened. The said separation of the movements gives also the additional effect that the apparatus easily can be set for different radii of the tube bends.

The invention will now be explained in greater detail in the following specification, describing an embodiment of the invention and comprising the following drawing figures:

FIG. 1 is a top view of a shot peening device according to the invention;

FIG. 2 is a side view of the peening device;

FIG. 3 is section 3-3 in FIG. 2 drawn on a larger scale; and

FIGS. 4 and 5 are different patterns of the effective areas of the peening jets.

The figures show a device according to the invention for shot peening U-shaped tubes for heat exchangers in, for instance, atomic power plants. The starting position before peening is shown in full lines in FIG. 1. The tube 10 rests on a bed of rollers 11 and the curved portion of the tube is held by a gripping arm 12 on a sledge 13, which can move along a guide 14. A shot peening nozzle assembly 15 is placed in the extension of the shank of the tube shown as the upper shank in the figure. The nozzle assembly 15 is shown in a side veiw on a larger scale in FIG. 3. It comprises a number of shot peening nozzles, placed concentrically around a center and directed towards the center. The nozzle set is mounted on a bracket 17, which can be turned on a vertical axis 18. The nozzles are, in practice, associated with the conventional hoses (not shown) for delivering the necessary jets of peening shot.

The peening is performed by blowing particles, for instance glass balls, through the nozzles 16 against the center of the nozzle assembly 15. The sledge is moved by a mechanism along the path 14, so that the shank 20 of the tube 10 passes through the nozzle assembly 15.

When the tube 10 has arrived at the position 10a, drawn in dashed line, the sledge 13 is stopped. During the subsequent phase of the process the nozzle assembly 15 is swung along the tube bend 21 in the direction of the arrow 23 to the position 15a, and during this movement the bend is shot peened. In order to permit the peening device to pass the holder 12 the holder can be temporarily let down to the position 12a.

In the third phase of the procedure the nozzle assembly is held stationary in the position 15a, and the sledge 13 is moved back to its starting position. During this movement the other shank 22 of the tube is shot peened. The sledge device 12, l3, 14 may alternatively be placed above the tube, as shown in broken lines 12a, 13a, 14a in FIG. 2, in order to have a clear floor surface.

The distance between the axis 18 and the center of the nozzle assembly should, of course, be the same as the radius of the tube bend. For adaption to bends with different radii the nozzle assembly 15 can be moved on the bracket 17 towards, or away from, the axis 18. As shown in FIG. 3, assembly 15 may be removably secured to bracket 17, by means of a bolt 30, and assembly 15 may be moved from one location toward, or away from, axis 18 by securing it to the bracket at one or another of a plurality of spaced bolt holes 31, 31 as shown in FIG. 3. In FIG. 1 is shown in dashed lines a tube 10b having a bend with a greater radius, the nozzle set having .to be moved to the position 15b. For different radii of curvature, of course, also the left hand position in FIG. 1 of the sledge 13 has to be adjusted so that the center of the bend coincides with the rotation axis 18 of the nozzle assembly.

When shot peening is performed on straight tubes without bends the tube is usually rotated on its axis at the same time as it is fed axially through the peening apparatus. The purpose of this is to distribute the peening effect as uniformly as possible. When peening is performed on tubes with bends it is, of course, impossible to rotate the tube on its axis. Because of this, other means must be used to provide for uniform peening effect around the tube. As the peening jet is conical and has a circular cross section it is difficult to obtain a uniform effect if the axii of the nozzles 16 lie in the same plane because the areas of action of the peening jets must partly cover each other as shown in FIG. 4, in order to cover the whole periphery. The result of this is that adjacent jets interfere with each other, and particles dash against each other thus lessening the efficiency within the area covered by two adjacent jets. In order to avoid this the peening jets are given a slight inclination sideways, every first jet being inclined towards one side and every second towards the other side. In this manner the effective areas of the jets become distributed in the way shown in FIG. with substantially less interference between the jets.

We claim:

1. Method of shot peening the external surface of a tube that is partly straight and partly curved, using an assembly of shot peening nozzles arranged concentrically around and directed towards the tube, according to which for shot peening a straight portion of the tube the nozzle assembly is held stationary and the tube is moved in a straight path with said straight portion passing through the nozzle assembly, while for shot peening a curved portion of the tube the tube is held stationary and the nozzle assembly is moved about the curved portion.

2. Device for shot peening the external surface of a partly straight and partly curved tube, said device comprising a nozzle assembly having a number of shot peening nozzles that are concentric with the tube and directed towards the tube, means for moving the tube in a straight path thereby passing a'straight part of the tube through the nozzle assembly. and means for moving the nozzle assembly about a bend of the tube.

3. Device as defined in claim 2, wherein the means for moving the nozzle assembly includes means for setting of different radii for the movement.

4. Device as defined in claim 2, wherein the means for moving the tube in a straight path comprises a tube holder that is moved in a straight path.

5. Device as defined in claim 4, in which the holder for moving the tube in a straight path is placed above the tube.

6. Device as defined in claim 2, wherein adjacent shot peening nozzles are set at slightly different angles in relation to the axis of the tube in order for less interference between the jets.

7. Device as defined in claim 6, in which every first nozzle is somewhat inclined to one side and every second nozzle to the other side of the nozzle assembly.

l l= l UNITED STATES PATENT OFFICE CERTHHCATE(HTCORRECTHMN PATENT NO. 1 3,886,77 4

DATED June 3, 975

INVENTOR(S) I Sven Sixten Stromstedt and Sven Borje Bystrom It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

. [73] Assignees: Sandvik-Aktiebolag,

Sandviken, Sweden Kraftwe rk Union Aktiengesellschafc, hulheim, Ruhr;

. Manne smann roh Pen-We rke Akt ie nge sells chaft Dusseldorf both of Ge rmany Signed and Scaled this fourth D 3) Of November 1975 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner oflarents and Trademarks 

1. Method of shot peening the external surface of a tube that is partly straight and partly curved, using an assembly of shot peening nozzles arranged concentrically around and directed towards the tube, according to which for shot peening a straight portion of the tube the nozzle assembly is held stationary and the tube is moved in a straight path with said straight portion passing through the nozzle assembly, while for shot peening a curved portion of the tube the tube is held stationary and the nozzle assembly is moved about the curved portion.
 1. Method of shot peening the external surface of a tube that is partly straight and partly curved, using an assembly of shot peening nozzles arranged concentrically around and directed towards the tube, according to which for shot peening a straight portion of the tube the nozzle assembly is held stationary and the tube is moved in a straight path with said straight portion passing through the nozzle assembly, while for shot peening a curved portion of the tube the tube is held stationary and the nozzle assembly is moved about the curved portion.
 2. Device for shot peening the external surface of a partly straight and partly curved tube, said device comprising a nozzle assembly having a number of shot peening nozzles that are concentric with the tube and directed towards the tube, means for moving the tube in a straight path thereby passing a straight part of the tube through the nozzle assembly, and means for moving the nozzle assembly about a bend of the tube.
 3. Device as defined in claim 2, wherein the means for moving the nozzle assembly includes means for setting of different radii for the movement.
 4. Device as defined in claim 2, wherein the means for moving the tube in a straight path comprises a tube holder that is moved in a straight path.
 5. Device as defined in claim 4, in which the holder for moving the tube in a straight path is placed above the tube.
 6. Device as defined in claim 2, wherein adjacent shot peening nozzles are set at slightly different angles in relation to the axis of the tube in order for less interference between the jets. 